JPS5883599A - Driving device for step motor - Google Patents

Abstract

PURPOSE:To improve the power efficiency of a step motor by controlling the exciting current by the reference voltage made of high and low level binary values, thereby reducing the consumed power. CONSTITUTION:A reference voltage generator 21 outputs a binary reference voltage to become high level during the prescribed period synchronously with the exciting signal of a field coil 28 and to become low level after the prescribed period. An exciting current detector which includes an exciting current detedting resistor R8 produces the detected voltage in response to the exciting current of a field coil 28. A comparator 24 compares the detected voltage with a reference voltage, thereby controlling a chopper circuit which includes a chopper transistor 27 by the output signal of the comparator. Since the exciting current of a step motor field coil 28 is controlled in response to the reference voltage made of high and low binary values, the current at the time of holding the position can be sufficiently reduced.

Description

[Detailed description of the invention] The present invention relates to a step motor drive device.

A step motor is a type of control equipment that converts electrical pulses of input signals into mechanical displacement, and has features such as fast response speed, excellent angular resolution, and high reliability.

In recent years, as computers and ICs have become widespread and digital information processing has become easier and more economical, step motors have come to be widely used as actuators in digital control systems that require high speed, high precision, and high reliability. There is.

Control devices for automobiles and the like are also becoming increasingly digitally controlled using microprocessors, and step motors are being used as actuators.

It is known that the characteristics of step motors are not only affected by the type of motor but also greatly influenced by its energization method and drive method. Accordingly, various driving methods have been devised, and representative ones include a series resistance method, a two-voltage method, and a chopper method.

Particularly required conditions for application to a control device for an automobile include the ability to be driven by a single battery power source and low power consumption.

Although the series resistance method has a simple circuit configuration and excellent responsiveness, it has the drawback that power loss in the resistance section is extremely large.

The dual pressure method was devised as a drive method that can increase the response speed of a step motor and reduce power consumption. Figure 1 shows a drive circuit for one phase of a step motor using this method. Give an example.

As shown in the figure, a high voltage power supply 3 and a low voltage power supply 5 are connected through a transistor 2 and a diode 4, respectively, to the positive terminal of the field winding 1 of the step motor. The negative terminal of the field winding 1 is grounded via the transistor 6, and the negative terminals of the high voltage power supply 3 and the low voltage power supply 5 are grounded.

The terminal 7 to which the excitation signal of the field winding 1 is input is connected to the pace of the transistor 6 and the monostable multivibrator 8 (
(hereinafter abbreviated as MMB) is connected to the input terminal of the
The output terminal of the MMBg is connected to the base of the transistor 20.

As configured as above, C) the excitation voltage vP- of the field winding 1 can be switched to a high voltage or a low voltage by turning on or cutting off the transistor 2 as desired. can. Now, when the excitation signal shown in FIG. 2 (5) is input, the transistor 6 passes through the T time slot, and at the same time, the signal shown in FIG. Conducted. As a result, a high voltage is applied to the field winding 1 as shown in FIG. 6, and a large excitation current I, shown in FIG. receives a large torque and begins to displace. +1+■ hours later, MM
When the output signal of B8 becomes zero, the transistor 2 is cut off, the excitation voltage vP of the field winding 1 is switched to a low voltage, and the excitation current IP is reduced. After 1 hour, when the excitation signal becomes zero, the transistor 6 is cut off and the field winding 1 is de-energized.

The step motor is rotated by a predetermined displacement within one hour, and after the displacement is completed, the exciting current generates torque to maintain the position.

In this way, the power supply system improves the response speed for high-voltage starting and switches to a low voltage after a predetermined time, thereby suppressing heat generation in the windings and reducing current consumption by reducing position holding current. It is something.

However, since it requires two types of power sources, a high-voltage power source and a low-voltage power source, it has the disadvantage that it cannot be applied to automobiles and the like that are equipped with only a single power source.

As an example of a chopper type drive circuit, the one shown in FIG. 3 is known.

The figure shows a drive circuit for one phase.The positive terminal of the field winding 11 is connected to the positive pole of the power supply 13 via the chopper transistor 12, and the negative terminal of the field winding 11 is used for current detection. It is grounded via a resistor 14. The differential amplifier 15 (
-) input terminal is connected to the triangular wave generation circuit 16, and (+)
The input terminal is connected to a point P on the positive side of the current detection resistor 14. The output terminal of the differential amplifier 15 is connected to the base of a transistor 18 via a resistor 17, and the collector of the transistor 18 is connected to the base of the chopper transistor 12 and the positive terminal of a power supply 713 via a resistor 19. are connected to each. Further, the emitter of the transistor 18 is grounded. The positive terminal of the field winding 1 is grounded via a freewheeling diode 20.

The operation will be explained below.

The triangular wave generation circuit 16 is formed of a circuit that outputs a DC reference voltage vR on which a small amplitude triangular wave shown in FIG. 4(F) is superimposed when an excitation signal having the waveform shown in FIG. 4(E) is input. has been done. The differential amplifier 15 has a large gain, and the two input to the (-) input terminal and (+) input terminal
When the difference between the two input voltages is negative, a low level voltage signal is output, and when the difference between the two input voltages is positive, a high level voltage signal is output. [ of the differential amplifier 15
−] The reference voltage vR is input to the input terminal, and (+)
A detected voltage vI, which is proportional to the voltage at point P, that is, the excitation current of the field winding 11, and is shown by a broken line in FIG. 4(F) is input to the input terminal. Initially when the excitation signal is input, Vi+>Vr'
Therefore, a low-level voltage signal is output from the differential amplifier 15, and the chopper transistor 12 is made conductive via the transistor 18. This causes the field winding 11 to have a power supply voltage v! I is applied to the field winding 11 as shown in FIG.
), the excitation current I has a steep rise.

flows. As the excitation 5vl current I increases, the detection voltage VI rises, and when it reaches vI, a high level voltage signal is output from the differential amplifier 15 and the chopper transistor 12 is cut off. In this way, by comparing the reference voltage vR and the detection voltage vf and turning on and off the Tejoch transistor 18, the chopper-controlled voltage V is applied to the field as shown in FIG. 4(G). applied to the winding.

Therefore, according to the chopper type drive circuit, by starting the step motor with the full voltage of the power supply and flowing a steep starting current at startup, a large drive torque is generated and the response speed is increased, and after starting, the step motor is By adjusting the voltage according to the excitation current, the step motor can be driven with high power efficiency even with a single power source.

However, the set value of the reference voltage ■R is 1 value, and it cannot be set too low to obtain the required starting characteristics, so it is not possible to sufficiently reduce the current consumption during position holding, which does not require much torque. It has the disadvantage of not being possible.

Furthermore, since a triangular wave generation circuit is required, the drive circuit has the disadvantage of becoming complicated.

An object of the present invention is to provide a step motor drive device that can simplify the circuit configuration, reduce power consumption, and improve power efficiency.

The present invention provides a chopper circuit connected to a field winding of a step motor, and a binary reference voltage that is at a high level for a predetermined period and becomes a low level after the period in synchronization with the applied field winding excitation signal. - an excitation current detection circuit that outputs a detected voltage according to the excitation current of the field winding; a comparator that compares the detected voltage with the reference voltage; Self-excited oscillation is achieved by connecting a resistor between the output terminal of the device and the input terminal into which the reference voltage is input.
The circuit configuration is simplified and power consumption is reduced by controlling the seven return ports that superimpose the small amplitude alternating current of 1 on the reference voltage and the chopper circuit that controls the output signal of the comparator. This is intended to improve power efficiency.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 5 shows a circuit diagram of an embodiment of the present invention.

The illustrated circuit is a drive circuit for the 1st and 3rd phases of a bifilar-wound, 4-phase step motor, and the energization method is applied so that the 1st and 3rd phases are not excited at the same time. The chopper circuit etc. can be shared. The explanation will be given only for the first phase.

Monostable 1 multi-bicycle brake 22 of reference voltage generation circuit 21
A first phase excitation signal is input to the MMB (hereinafter abbreviated as MMB), and an output signal of the MMB 22 is input to the transistor 230 through a resistor. A control power source VC is applied to the collector of the transistor 23 via a series resistor R and a resistor R3, and the collector is grounded via a resistor R3.

Further, the emitter of the transistor 23 is grounded. A resistor R4 is connected to the connection point between the series resistors R1- and R2.
It is connected to the (+) input terminal of the comparator 24 via. The (+) input terminal is connected to the output terminal of the comparator 24 via a feedback resistor R5. The output terminal is resistor R
6 to the control power supply VC, and to the base of the transistor 25 via a resistor R7. The collector of the transistor 25 is connected to the positive electrode of a battery 26 via a resistor, and to the base of a chopper transistor 27 via a resistor. The emitter of transistor 25 is grounded. The emitter of the chopper transistor 27 is connected to the positive electrode of the battery 26, and the collector is connected to the collector of the phase switching transistor 30 via a diode 29 connected in series with the field winding 28 in the forward direction. The emitter of the transistor 309 is grounded via an excitation current detection resistor R8, and the ground side of the resistor R8 is connected to the (-) input terminal of the comparator 24.

An excitation signal for the field winding is input to the base of the transistor 3o via a resistor.

The positive end of the field winding 28 is grounded via a freewheeling diode 31 connected in the opposite direction.

The operation will be described below using the time chart shown in FIG.

When a pulse signal, which is a displacement command, is given to the step motor, excitation signals for each phase are input to the drive device in accordance with the pulse signal. 1st phase and 3rd phase when using two-phase excitation method
The phase excitation signals have waveforms shown in (J) and (K) in FIG.

The excitation signal (
J), the phase switching transistor 30 is turned on and at the same time, the monostable multivibrator (MMB) 2 is turned on.
2, a voltage signal in which the TH output voltage becomes zero for a predetermined period of time shown in FIG. 2(L) is output. By this signal? ) lunge,
The star 23 is shut off for lllH time. At this time, the voltage at the point, that is, the reference voltage V RFi, the resistance ratio 4, Rs
Since the resistors ``+'', R2, and ``1'' are selected to be sufficiently large, the high-level reference voltage (VR) M is expressed by the following equation (1).

(VR)'H'p ("2 +"!) VC/ (R
1+"2+"3)... (1) Next, after lllH time, when the transistor 23 is turned on, the reference voltage ■E becomes low as expressed by the following equation (2).

The reference voltage (VR) is L. .

(VR)t, *kL2vc/ (R1+R2)---”
Therefore, the reference voltage VR is input to the comparator 24 as a voltage signal having the waveform shown in (N) in the figure.

The comparator 24 also receives the detection voltage I detected by the excitation current detection resistor FL8, and compares it with the reference voltage VR. When the reference voltage (VR) M is input, no excitation current is flowing, so (Vu)i>Vr
It is. At this time, a trigger signal is output from the comparator 24, and the chopper and the transistor 27 are made conductive via the transistor 25. As a result, an exciting current I is applied to the field winding 28.

flows and the step motor is started. Excitation current I.

is quickly ramped up by the full battery voltage.

Correspondingly, the detection voltage increases and when VR)11<VI, the output trigger signal of the comparator 24 becomes a low level, the chopper transistor 27 is cut off, and the excitation current I,
decreases. Part 1. decreases, the detection voltage decreases, and (V
R) When H>vX, the comparator outputs a trigger signal again, and the above-described operation is repeated.

The above-mentioned detection voltage V! Due to the transient fluctuation of , self-oscillation occurs in the circuit formed by the comparator 24 and the hysteresis resistors R, , R, and a square wave voltage having a hysteresis width H expressed by the following equation (3) is oscillated. Ru.

"R4VC/("4+"II) ---(3) This square wave voltage is the reference voltage ■R of the comparator 24 input (
Since it is input to the (+) input terminal of the comparator 24, the (+)
) The signal input to the input terminal becomes a signal voltage VD having a waveform in which a square wave voltage with a small amplitude is superimposed on the reference voltage vR, as shown in (Q) in the figure.

Therefore, in the comparator 24, this signal voltage VD and the detection voltage V
! A trigger signal is output when Va>Vr. The conduction rate of the chopper transistor is controlled by the trigger signal, and the excitation current 11 is controlled in accordance with the reference voltage va.

Further, after the predetermined time T has passed, the output voltage of the MMB 22 is no longer high, the transistor 23 is turned on, and the reference voltage becomes the low level reference voltage (Vg)t.

As a result, the excitation current I is reduced.

As mentioned above, the excitation current I of the step motor field winding
l' is controlled according to the reference voltage v11 consisting of two values of high and low levels, and as shown in FIG. 6(P), lllH
After that time, it becomes sufficiently reduced.

Note that the frequency of the trigger signal that controls the chopper transistor, the so-called chopper frequency, is determined by the rise of the current due to the hysteresis width H and the time constant of the field winding.
By changing the ratio of the hysteresis resistors kL4 and R6, the chopper frequency can be changed arbitrarily.

Therefore, according to this embodiment, since the excitation current is controlled by a reference voltage consisting of two values of high and low levels, the starting current for a steep start-up is ensured, while the current for holding a position is controlled. It is possible to sufficiently reduce heat generation in the field winding, reduce power consumption, and improve power efficiency.

Further, according to this embodiment, when driving at low speed, l1lH
Since T becomes relatively long, the average excitation current becomes small, and the effect of reducing power consumption is promoted.

Furthermore, according to this embodiment, since a self-oscillation function consisting of a simple circuit is provided, a triangular wave generation circuit is not required, which simplifies the circuit of the drive device and improves the reliability and economy of the device. is improved.

As described above, according to the present invention, it is possible to simplify the circuit configuration, reduce power consumption, and improve power efficiency.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional example, Fig. 2 is an explanatory diagram of the operation of the conventional example shown in Fig. 1, Fig. 3 is a circuit diagram of another conventional example, and Fig. 4 is an explanation of the operation of the conventional example shown in Fig. 3. 5 is a circuit diagram of an embodiment of the present invention, and FIG. 6 is an explanatory diagram of the operation of the embodiment shown in FIG. 21... Reference voltage generation circuit, 24... Comparator, 27
...Chopper transistor, 28...Field winding, 2
6...Y 4 Fake

Claims (1)

[Claims] 1. In synchronization with the input step motor excitation signal, the voltage is high for an initial predetermined period of time and becomes low voltage after the predetermined period of time 2.
a reference voltage generation line capable of outputting a reference voltage formed from the voltage level of the step motor; an excitation current detection circuit capable of outputting a detection voltage corresponding to the excitation current of the step motor field winding; a self-excited oscillation circuit that oscillates an alternating current voltage formed by connecting a resistor between an output terminal of the comparator and an input terminal to which the reference voltage is input; and a step motor. a chopper circuit connected to a field winding of the step motor, and the chopper circuit is controlled by an output signal of the comparator.